The objective of the proposed project is to understand the role of non-pyrimidine dimer damage in the biological effects of ultraviolet irradiation. This study will make use of a DNA-binding protein isolated from human placenta and specific for non-dimer UV- or X-ray induced damage. My approach to this problem will involve purifying large quantities of this protein and using it to isolate non-dimer damage from irradiated DNA. This will be accomplished by protecting the damage with binding protein while the DNA is hydrolyzed to oligonucleotide fragments. Protein-bound fragments will be isolated on nitrocellulose filters and the nature of the damage will be determined with a variety of chemical probes. In addition, the fate of the non-dimer damage in irradiated cells will be examined by using the binding protein as a probe for the presence of such damage in the DNA. In these studies, a variety of UV-sensitive bacterial mutants will be examined as well as human fibroblasts derived from patients with xeroderma pigmentosum. This work should extend our understanding of the processes involved in DNA damage and repair to systems which deal with damage other than pyrimidine dimers.